SB Cast Iron Exhaust Manifolds

I will be using cast iron manifolds on my 360 going into my '67 Cuda.

Here are the casting numbers:

Pass. side 3418623
Dr. side 3614395

My Mopar dot com lists these manifolds for the 1971-73 Dart 340's

My question is this:

Why would the discharge port be smaller on the driver's side. Did the factory
use two different size "ball flanges" on the front pipes? Any info would be
appreciated.

Thanks